A terror warning has prompted Israelis to cut short vacations in neighboring Egypt.

Hundreds of Israelis vacationing in Egypt's Sinai Peninsula have returned home after Israel issued an urgent terror alert. The warning said there is "concrete evidence" of an imminent attempt by terrorists to kidnap Israelis in Sinai.

Brigadier-General Nitzan Nuriel, the head of Israel's counter-terrorism agency, said the warning is based on hard intelligence.

Nuriel said it is possible that at this very moment a terrorist cell has completed preparations to kidnap an Israeli and smuggle him into the Hamas-ruled Gaza Strip, which shares a border with Sinai. Hamas, an Islamic militant group, has been holding an Israeli soldier for nearly four years in Gaza, and additional hostages could be used as bargaining chips to win the release of Palestinian prisoners.

Officials say about 650 Israelis were in Sinai when the warning was issued late Tuesday, and most have returned home.

Tens of thousands of Israelis visit Sinai each year, enjoying the beautiful desert beaches of the Red Sea, unspoiled coral reefs and cheap prices. They simply ignore this Hebrew-language warning at the border crossing.

Broadcast over loudspeakers, the warning urges Israelis not to visit Sinai because of terror threats.

But Israelis heeded the latest warning because it was unusual and especially urgent. Family members were urged to call their relatives in Sinai and tell them to return home.

Egyptian resorts in the Sinai Peninsula have been hit by several terrorist bombings, the last in 2006. The attacks were a blow to tourism; in addition to Israelis, Sinai is a popular spot for European tourists. Egyptian security sources played down the Israeli warning, saying Sinai is a safe place to visit.